Tails?

Top Voted Answer

I think I can help you here. There are a total of six different colors of Tails (except the Rat Tail, which is an entirely different story): Yellow, Green, Blue, Black, Red, and Pink. When you get a Tail, you must take them to the Tail trader on Adamant Isle (on the overworld map, it is in the central-right area of the map; you must use the Enterprise and carry the Hovercraft to there, and use the Hovercraft to get in the cave there, and then you may talk to the short man on the small pedestal, and give him the Tail(s).

Each colored Tail gets you a different item, most of which are generally considered the best equips in the game (to be mentioned shortly), except for the Rat Tail, of course, in which you get in the Feymarch (a cave in the center-west area of the underworld), and give to the Tail trader to get a piece of Adamantite (which you are to take to the blacksmith, who is in the house to the far south-east in the underworld). You'll understand the rest of that side-quest after doing that... As for the COLORED Tails, you must fight a specific type of enemy and win it from a random drop after the battle, which are these (as well as where to Siren said enemy for easy tail-hunting):

Yellow - Yellow Dragon (Siren near the Cave of the Eidolons)Green - Green Dragon (Siren near the town of Tomra, which is far-south in the underworld)Blue - Thunder Dragon (Siren in the Cave of the Eidolons, room B3, which is the room where the teleport to the Feymarch is)Black - Armored Fiend (Siren in the second Room of the Lair of the Father, which is to the far-east on the moon)Red - Red Dragon (Siren in the Lunar Subterrane, B10? [the room where the background changes dramatically, which is also where you cannot teleport out from)Pink - Flan Princess (Siren in the room that is in the south-east corner of room B7 of the Lunar Subterrane, which [as a help to its location] has a chest with a Red Fang inside of it)

As for what you get by bringing the Tails to the Tail trader, these are the items you get (and their effect):

So far, the Onion Sword, the Onion Shield, and the Adamant Armors are the only REAL good items there, the Onion Sword being able to be the most powerful weapon Cecil and Kain can use, the Onion Shield because it nullifies all status ailments except Berserk (only Crystal Armor can negate that), and the Admant Armor because... well, it gives 100 Defense AND Magic Defense (even at level 1), increases all attributes by 15, and nullifies almost every status ailment you can get, except a few minor ones like Sap and Slow.

As for the best ways to get them... well, you might as well just ask around, or perhaps I might be able to answer that later on if this question is still up by then.

To continue Chaosmaster's answer, the best way to get them is to move sirens to the top of your items, save, and just keep using them and defeating the monsters until you get one. If you use all your sirens, just reset and keep trying. The treasure hunter augment will also increase the chance of a tail drop for .4% to .8%